Cucumber Downy Mildew Control in a Challenging Season

Last week’s confirmation of downy mildew in both Kent and Elgin was unusually early. Recent reports have also been made in Michigan and Ohio. As a result, we are in the unfortunate situation of having to “stay ahead” of the disease this year. Here are a few additional thoughts to help manage this aggressive disease in what appears to be a high pressure year.

Rotate! Research at Ridgetown Campus has shown that the “best” product does vary from year-to-year, and that all of the products have had years where they did not perform as well. To rely on one or even two products puts the crop at risk should one of those products fail, or if resistance develops. Use at least 3 different products from different fungicide groups.

If at all possible, spray BEFORE aforecast rain event. While several of the products have a limited amount of curative properties, they all work best when used preventatively.

If downy mildew is present in your field, shorten the spray interval. Especially if rain is forecast in the immediate future (see above).

All leaf material is susceptible to downy mildew infection, even the cotyledons. Begin a preventative program in new plantings as soon as they emerge.

Scout fields regularly, especially fields in which downy has not yet been identified. And by regularly, I mean daily! The disease can progress significantly in just a few days. I have seen fields go from “watersoaked” lesions to spore producing brown lesions in less than one day.

Ranman 400SC/Torrent 400SC

In response to the issue regarding the use of Ranman 400SC the PMRA has issued this response: “The RANMAN 400SC AGRICULTURAL FUNGICIDE (Reg. No. 30716) was recently amended to remove all uses except potatoes. With respect to product bearing the previous label,(i.e. just prior to the latest amendment), the PMRA would have no issue with this previously purchased product being used on cucumbers for the 2015 use season. Any purchase of product bearing the newly amended label however, will ‎need to be used in accordance with the new label.”

Moving forward, cucurbit growers are reminded that Torrent 400SC is now the registered formulation of cyazofamid for the control of downy mildew in this crop.